netdev - RE: [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF

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Message-ID: <5f68caed36dab_17370208e9@john-XPS-13-9370.notmuch>
Date:   Mon, 21 Sep 2020 08:46:53 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Tony Ambardar <tony.ambardar@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Tony Ambardar <Tony.Ambardar@...il.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-arch@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: RE: [PATCH bpf v1 3/3] libbpf: fix native endian assumption when
 parsing BTF

Tony Ambardar wrote:
> Code in btf__parse_raw() fails to detect raw BTF of non-native endianness
> and assumes it must be ELF data, which then fails to parse as ELF and
> yields a misleading error message:
> 
>   root:/# bpftool btf dump file /sys/kernel/btf/vmlinux
>   libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
> 
> For example, this could occur after cross-compiling a BTF-enabled kernel
> for a target with non-native endianness, which is currently unsupported.
> 
> Check for correct endianness and emit a clearer error message:
> 
>   root:/# bpftool btf dump file /sys/kernel/btf/vmlinux
>   libbpf: non-native BTF endianness is not supported
> 
> Fixes: 94a1fedd63ed ("libbpf: Add btf__parse_raw() and generic btf__parse() APIs")
> 
> Signed-off-by: Tony Ambardar <Tony.Ambardar@...il.com>
> ---
>  tools/lib/bpf/btf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 7dfca7016aaa..6bdbc389b493 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -659,6 +659,12 @@ struct btf *btf__parse_raw(const char *path)
>  		err = -EIO;
>  		goto err_out;
>  	}
> +	if (magic == __bswap_16(BTF_MAGIC)) {
> +		/* non-native endian raw BTF */
> +		pr_warn("non-native BTF endianness is not supported\n");
> +		err = -LIBBPF_ERRNO__ENDIAN;
> +		goto err_out;
> +	}
>  	if (magic != BTF_MAGIC) {
>  		/* definitely not a raw BTF */
>  		err = -EPROTO;
> -- 
> 2.25.1
> 

Acked-by: John Fastabend <john.fastabend@...il.com>